The control and maneuvering of modern high speed aircraft remains a technical area in which designers continue to press for ever-increasing effectiveness. Such increased control response may require a balancing with increased airframe drag as control surfaces become larger, while in certain flight regimes, such as in supersonic or low-speed flight, the effectiveness of even large surfaces is diminished for certain angles of attack, etc.
One effective method for imparting additional maneuvering force is the use of a thrust vectoring exhaust nozzle. Such nozzles divert the flow of exhaust gas from the aircraft propelling gas turbine engine at an angle from the normal exhaust flow, thereby developing asymmetric thrust (and hence moment) with respect to the airframe center of gravity. Simpler versions of such thrust vectoring nozzles are able to impart thrust vectoring with respect to a single axis, for example the pitch axis. Such simpler versions still require several cooperating gas directing surfaces, especially convergent-divergent thrust vectoring nozzles used in conjunction with gas turbine engines equipped with an afterburner. The convergent section of such nozzles must be adapted to provide a variable throat area for optimization of the engine thrust, while the divergent section directs the exhaust gas selectably in the vertical plane for pitch thrust vectoring.
Yaw and pitch thrust vectoring exhaust nozzles are also known in the art, and are able to divert the exhaust gases in both the horizontal and vertical plane, thus achieving two axis thrust vectoring. Such two axis nozzles require additional structure and complexity over the one axis designs, requiring the advantages of increased maneuverability to be balanced against the additional weight and complexity required.
One advantage which thrust vectoring designs achieve with respect to prior art unvectored engine exhaust systems is the reduced control surface requirement for normal and even emergency maneuvering. The use of thrust vectoring exhaust nozzles in conjunction with automatic attitude control systems can achieve stable aircraft operation and control with reduced external control surfaces. Hence, an airframe having even a pitch thrust vectoring exhaust nozzle may operate with reduced size elevators providing benefits in external drag reduction, weight, etc. Likewise, a nozzle having yaw thrust vectoring capability can provide the necessary yaw maneuvering and stability to the airframe while permitting a reduction in rudder size.
A third axis of control remains which has no been adequately addressed by the prior art nozzle designs. The roll axis, traditionally controlled by ailerons on the aircraft wings, has thus far not been practically addressed by prior art thrust vectoring nozzles. What is needed is a thrust vectoring exhaust nozzle able to provide complete three axis thrust vectoring to an airframe, thereby achieving satisfactory control and stability with a reduced requirement for external control surface action.